JPH06283424A - Molecular beam epitaxial growth method and apparatus therefor - Google Patents

Abstract

PURPOSE:To make it easy to add dopant in the epitaxial growth. CONSTITUTION:A radical molecular beam emission cell 30 which supplies a dopant is provided with a hot cathode filament and a grid. Electrons emitted from the hot cathode filament are accelerated by the voltage applied between the hot cathode filament and the grid, and caused to strike the dopant material introduced in the radical molecular beam emission cell 30 to produce a radical molecular beam.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a molecular beam epitaxial growth method and apparatus, and more particularly to a molecular beam epitaxial growth method and apparatus for growing an epitaxial crystal of a compound semiconductor while introducing a dopant into the compound semiconductor to be epitaxially grown.

[0002]

2. Description of the Related Art Molecular beam epitaxy is used for epitaxial growth of compound semiconductors.
y, MBE) (hereinafter referred to as MBE method) and metal organic chemical vapor deposition method (Metal Organic Chemical Vapor Depos
ition, MOCVD) (hereinafter referred to as MOCVD method) and the like are generally used.

Among them, the MBE method is capable of controlling the thin film to be grown at the atomic or molecular level, and is excellent in the steepness and flatness of the hetero interface in the epitaxial growth (hetero growth) of different materials. , It is extremely advantageous for fabrication of quantum wells and superlattice structures, which can be expected to be applied to higher output and shorter wavelength. Further, it has industrial advantages such as extremely high material utilization efficiency.

In the MBE method, an ultrahigh vacuum, for example, 1
A semiconductor substrate is placed in a reaction chamber having a pressure of 0 ^-7 to 10 ^-10 torr, and a raw material for a semiconductor thin film to be grown is placed in a container called an ejection cell which is arranged with its outlet facing the reaction chamber. Is supplied. The Knudsen cell or the like is typical as the ejection cell. By heating the raw material in the ejection cell, the raw material evaporates in a vacuum in the form of molecules (or atoms), which becomes a beam of molecules directed in a specific direction, that is, directed to the semiconductor substrate. The molecules supplied and reaching the semiconductor substrate form a semiconductor thin film.

More recently, a gas source molecular beam epitaxy (GSMBE) method (hereinafter referred to as a GSMBE method) in which a gas is introduced as a raw material in the MBE method has been proposed.

By the way, as an example of epitaxial growth of II-VI group compound semiconductors, gallium arsenide (GaA) is used.
s) A method of growing an epitaxial crystal of zinc selenide (ZnSe) on a substrate and introducing nitrogen (N) as a dopant (impurity) to obtain a p-type crystal is described in Appl. Phys. 5
7 , 2127 (1991). In this way, M
In a BE apparatus, nitrogen is generated as a nitrogen radical molecular beam by an RF plasma cell to grow a low-resistance p-type zinc selenide thin film doped with nitrogen at 10 ¹⁸ cm ⁻³ level.

However, in order to generate a nitrogen radical molecular beam from nitrogen molecules using an RF plasma cell, it is common to set the atmospheric pressure condition to about 10 ^-1 to 10 ^-2 torr, but the MBE method is generally used. Applicable conditions are 10
^Since it is about ^-7 to 10 ^-10 torr, in order to maintain the pressure in the RF plasma cell, the exit port of the cell for irradiating the substrate surface with the nitrogen radical beam must be extremely small, It was not possible to irradiate a large area. There is also a problem that expensive peripheral devices such as a high frequency generator for generating plasma are required.

[0008]

SUMMARY OF THE INVENTION The present invention has been made in view of the problems of the prior art as described above.
It is an object of the present invention to provide a molecular beam epitaxial growth method and apparatus that facilitates the addition of a dopant in the epitaxial growth of Group VI compound semiconductors. The present invention is
In particular, it is an object of the present invention to provide a molecular beam epitaxial growth method and apparatus capable of adding a high concentration of nitrogen and growing a semiconductor compound in a large area.

[0009]

Means for Solving the Problems The above-mentioned objects are to supply a growth raw material by a molecular beam into a reaction chamber in which a substrate is placed, and use a radical molecular beam radiating cell to supply a dopant raw material to the substrate as a radical molecular beam. In the molecular beam epitaxial growth method of growing an epitaxial crystal of a compound semiconductor on the surface of the substrate while irradiating, a hot cathode filament and a grid are provided in the radical molecular beam emitting cell, and electrons emitted from the hot cathode filament are provided. A molecule characterized in that a voltage is applied between the hot cathode filament and the grid to accelerate electrons, which are excited by being made to collide with a dopant raw material to be converted into radical molecules, which are then irradiated to the substrate as a radical molecular beam. This is achieved by the linear epitaxial growth method. The molecular beam epitaxial growth method of the present invention is characterized in that the radical molecular beam amount is controlled by measuring the ion current of the ionized dopant raw material.

Further, the above-mentioned various objects are the source evaporation source for supplying the semiconductor source to be grown on the substrate placed in the reaction chamber, and the radical molecule for supplying the dopant as the radical molecule beam during the growth of the semiconductor film. In a molecular beam epitaxial growth apparatus having a beam emission cell, the radical molecular beam emission cell emits a cell case provided with a radical molecular beam emission port and a dopant raw material introduction port, and an electron provided in the cell case. It is achieved by a molecular beam epitaxial growth apparatus comprising a hot cathode filament and a grid for accelerating and controlling the emitted electrons.

The molecular beam epitaxial growth apparatus of the present invention is characterized in that an ion current collector for measuring the amount of ions is provided in the radical molecular beam emitting cell.

[0012]

According to the molecular beam epitaxial growth method of the present invention configured as described above, the radical molecular beam for supplying the dopant to the semiconductor film to be grown is electrically supplied to the hot cathode filament provided in the radical molecular beam emission cell. To heat the electrons, and accelerate and control the electrons emitted from them by applying a voltage to the grid to collide with the dopant raw material introduced into the radical molecular beam emission cell to excite the dopant raw material. , Which generate radical molecules to be supplied as a dopant.

Therefore, since radical molecules can be generated without being influenced by the pressure condition for plasma generation, the pressure inside the radical molecule beam radiating cell can be set to a high vacuum state as high as that in the reaction chamber. Therefore, the radiation port of the radical molecular beam can be made large, and irradiation of a large area can be achieved.

In the molecular beam epitaxial growth apparatus of the present invention, a hot cathode filament that emits electrons and an emitted electron are accelerated in a radical molecular beam emission cell that emits a radical molecular beam that supplies a dopant to a semiconductor film to be grown. Since it is configured with a control grid, a high frequency generator for plasma generation is unnecessary,
The device configuration can be simplified.

Further, the amount of radical electron beam supplied to the reaction chamber can be known as the current value of the amount of ions ionized when the dopant raw material is ionized by providing an ion current collector in the radical electron beam irradiation cell. Therefore, it is possible to directly know the generation amount of radical molecules. With this, it is possible to easily control the supply amount of the radical molecular beam by controlling the electron emission amount from the hot cathode filament, the acceleration amount of the emitted electrons, or the supply amount of the dopant raw material. .

[0016]

EXAMPLES The present invention will be described in detail below based on examples.

First, the molecular beam epitaxial growth apparatus of the present invention will be described. FIG. 1 is a schematic diagram of an embodiment of the MBE apparatus of the present invention.

The MBE apparatus 1 comprises a reaction chamber 2 including a liquid nitrogen shroud 10 for keeping the inside of the chamber in an ultrahigh vacuum state.
A substrate holder 3 made of graphite or the like, on which a substrate 20 for epitaxially growing a semiconductor film, which is provided inside the reaction chamber 2, is placed, and a fixture 11 for holding the substrate 20 placed on the holder 3. Raw material vaporization sources 4 and 5 such as Nukusen cells that supply the semiconductor film raw material as a molecular beam (or atomic form) and evaporate in the reaction chamber 2 to direct it to the substrate 20, and a radical molecule as a dopant. Radical molecular beam emission cell 30 for supplying as a beam. In addition, MB
The E apparatus is usually a manipulator for moving the substrate such as placing and removing the substrate 1, an ion gauge for measuring the amount of ions in the reaction chamber 2, a preparatory chamber for exchanging the substrate, and a reaction chamber 2.
A vacuum pump for decompressing the inside and the inside of the radical molecular beam radiating cell 30 and various electric wiring and piping for supplying raw materials,
Further, although an electron beam analyzer for observing the growth amount and state of the grown epitaxial film is provided as necessary, these are omitted in the drawing.

FIG. 2 is an enlarged view for explaining the radical electron beam emitting cell 30 provided in this MBE apparatus. The radical electron beam radiating cell 30 is provided with a cell case 31 provided with a radiant port 40 through which a radical molecular beam of a dopant is radiated toward the substrate 20 and a dopant raw material inlet 41 for guiding a dopant raw material gas into the radical molecular beam radiating cell 30. A hot cathode filament 32 for emitting electrons, which is housed in the cell case 31, a grid 33 for accelerating and controlling the emitted electrons, and a cell 3
Ion current collector 34 for measuring ion current in 0
And consists of.

The hot cathode filament 32 and the grid 33 are connected to lead wires 42 and 43, respectively, which supply necessary power from a power source (not shown), and the ion current collector 34 does not show the measured current value. A lead wire 44 for connecting to a control device or the like is connected.

Next, as an example of the molecular beam epitaxial growth method of the present invention, p-type zinc selenide (ZnSe) in which nitrogen (N) is introduced as a dopant on a gallium arsenide (GaAs) substrate using the above MBE apparatus. The method for growing the epitaxial crystal will be described.

First, the pressure in the reaction chamber 2 is set to 10 ^-9 torr.
Reduce the pressure to an ultra-high vacuum level. At this time, the pressure in the radical molecular beam emission cell 30 is drawn from the radical molecular beam emission port, and the dopant raw material is introduced into the radical molecular beam emission cell 30 during film growth.
It will be about 10 ⁻⁷ torr.

Then, the selenium and zinc set in the source evaporation sources 4 and 5 are heated and evaporated, and are released as molecules toward the substrate 20. At the same time, radical molecules of nitrogen, which is a dopant, are released from the radical molecular beam emitting cell 30 into the substrate. By radiating toward the p-type zinc selenide epitaxial crystal. The growth rate of the zinc selenide to be grown is 1 μm / h, the growth temperature is 300 ° C., and the dopant to be introduced is 0.5 cc / min of the amount of nitrogen gas introduced into the radical molecular beam emission cell 30.
In the case of, it becomes 7 × 10 ⁻¹⁷ cm ⁻³ .

Radiation of the nitrogen radical molecular beam from the radical molecular beam emission cell 30 is accelerated by heating the hot cathode filament 32 in the radical molecular beam emission cell 30 and drawing the emitted electrons into the grid 33. Then, by colliding with the nitrogen gas introduced from the dopant raw material introduction port 41 in the radical molecule beam radiating cell 30, the nitrogen molecules are excited to generate radical molecules. The voltage applied to the hot cathode filament 32 and the grid 33 for accelerating the electrons is
It is about 100 to 300V.

The control of the amount of nitrogen radicals during the growth of zinc selenide and the pressure in the radical molecular beam emitting cell 30 are provided in the radical molecular beam emitting cell 30,
The amount of positive ions generated when the nitrogen molecules are ionized is measured as a current by the ion current collector 34 applied with a voltage of about 10 to −40V. Based on this, the amount of nitrogen gas introduced into the radical molecule beam radiating cell 30 and the value of current flowing through the hot cathode filament 32 are controlled to control the amount of radical molecules generated. In addition, this ion generation amount is the cell 3
The condition that molecules in 0 do not cause multiple collisions (about 10 ^-4 to
rr or less), there is a proportional relationship with the amount of radical molecules generated.

As described above, by using the molecular beam epitaxial growth method and apparatus of the present invention, it is possible to grow a p-type zinc selenide crystal of low resistance and excellent film quality on a gallium arsenide substrate.

[0027]

As described above, according to the molecular beam epitaxial growth method and apparatus of the present invention, the radical molecular beam for supplying the dopant accelerates the electrons emitted from the hot cathode filament to collide with the dopant raw material. Since it is generated by excitation, it does not matter if the pressure in the radical molecular beam emission cell becomes an ultra-high vacuum state due to the decompression of the reaction chamber. Therefore, it is suitable for the MBE apparatus, and the RF plasma cell was used. As compared with the device, peripheral devices such as a high frequency generator are not needed, and the device configuration can be simplified.

Further, the generation amount of radical molecules can be directly known by the ion current collector provided in the radical molecule beam radiating cell.

[Brief description of drawings]

FIG. 1 is a schematic diagram for explaining a molecular beam epitaxial growth apparatus of the present invention.

FIG. 2 is an enlarged view of a radical molecular beam emission cell provided in the molecular beam epitaxial growth apparatus of the present invention.

[Explanation of symbols]

1 ... Molecular beam epitaxial device, 2 ... Reaction chamber,
3 ... Substrate holder, 4, 5 ... Raw material evaporation source, 10 ... Liquid nitrogen shroud, 11
... Fixing device, 20 ... Substrate, 30 ... Radical molecular beam emitting cell, 31 ... Cell case, 32 ... Hot cathode filament, 33 ... Grid, 34 ... Ion current collector, 40 ... Radical molecular beam emitting port, 41 ... Dopant raw material introduction Mouth, 42, 4
3, 44 ... Lead wire.

Claims (4)

[Claims] 1. A compound is deposited on a surface of a substrate while irradiating the substrate with a growth material by a molecular beam and irradiating the substrate with a dopant material as a radical molecular beam from a radical molecular beam emission cell. In the molecular beam epitaxial growth method for growing an epitaxial crystal of a semiconductor, a hot cathode filament and a grid are provided in the radical molecular beam emitting cell, and electrons emitted from the hot cathode filament are separated from the hot cathode filament and the grid. A molecular beam epitaxial growth method, characterized in that a voltage is applied between them to accelerate electrons, which are excited by being made to collide with a dopant raw material to be radical molecules, and the radical substrate is irradiated as a radical molecular beam. 2. The molecular beam epitaxial growth method according to claim 1, wherein the radical molecular beam amount is controlled by measuring an ion current of the ionized dopant raw material. 3. A raw material evaporation source for supplying a semiconductor raw material to be grown on a substrate placed in a reaction chamber, and a radical molecular beam emission cell for supplying a dopant as a radical molecular beam during the growth of the semiconductor film. In the molecular beam epitaxial growth apparatus having, the radical molecular beam emitting cell includes a cell case provided with a radical molecular beam emission port and a dopant material introduction port, a hot cathode filament for emitting electrons provided in the cell case, and A molecular beam epitaxial growth apparatus comprising: a grid for accelerating and controlling emitted electrons. 4. In the radical molecular beam emitting cell,
The molecular beam epitaxial growth apparatus according to claim 3, further comprising an ion current collector for measuring the amount of ions.